Ozone Layer Depletion

This section looks at the depletion of the ozone layer, causes of ozone layer depletion, effects of ozone layer depletion, ozone layer depletion solutions and ozone layer depletion facts. The latest ozone layer depletion news is included at the foot of the page.

Depletion of the ozone layer: the wearing out or destruction of the ozone in the stratosphere. The ozone layer is a belt of the naturally-occuring gas 'ozone' that sits at an altitude of between 15 and 30 kilometers above the Earth. It acts as a shield in protecting the Earth from harmful ultraviolet B (UVB) radiation.

Causes of ozone layer depletion

For nearly a billion years, ozone molecules in the atmosphere have protected life on Earth from the effects of ultraviolet rays.

The ozone layer resides in the stratosphere and surrounds the entire Earth. UV-B radiation (280- to 315- nanometer (nm) wavelength) from the Sun is partially absorbed in this layer. As a result, the amount of UV-B reaching Earth’s surface is greatly reduced. UV-A (315- to 400-nm wavelength) and other solar radiation are not strongly absorbed by the ozone layer. Human exposure to UV-B increases the risk of skin cancer, cataracts, and a suppressed immune system. UV-B exposure can also damage terrestrial plant life, single cell organisms, and aquatic ecosystems. Credit: www.theozonehole.com.

Ozone layer depletion background

Chlorofluorocarbons (CFCs) and other halogenated ozone depleting substances (ODS) are mainly responsible for man-made chemical ozone depletion.

CFCs were invented by Thomas Midgley, Jr. in the 1920s.

They were used in air conditioning and cooling units, as aerosol spray propellants prior to the 1970s, and in the cleaning processes of delicate electronic equipment.

They also occur as by-products of some chemical processes.

No significant natural sources have ever been identified for these compounds—their presence in the atmosphere is due almost entirely to human manufacture.

In 1974 Frank Sherwood Rowland, Chemistry Professor at the University of California at Irvine, and his postdoctoral associate Mario J. Molina suggested that long-lived organic halogen compounds, such as CFCs, would reach the stratosphere where they would be dissociated by ultraviolet light, releasing chlorine atoms.

In 1976 the United States National Academy of Sciences released a report concluding that the ozone depletion hypothesis was strongly supported by the scientific evidence.

Scientists calculated that if CFC production continued to increase at the going rate of 10 percent per year until 1990 and then remain steady, CFCs would cause a global ozone loss of 5–7 percent by 1995, and a 30–50 percent loss by 2050.

In response the United States, Canada and Norway banned the use of CFCs in aerosol spray cans in 1978.

Causes of ozone layer depletion

Ozone depletion describes two distinct but related phenomena observed since the late 1970s.

1) a steady decline in the total amount of ozone in Earth's stratosphere, and

2) a much larger seasonal springtime decrease in stratospheric ozone around Earth's polar regions. The role of sunlight in ozone depletion is the reason why the Antarctic ozone depletion is greatest during spring. During winter there is no light over the pole to drive chemical reactions.

During the spring, however, the sun comes out, providing energy to drive photochemical reactions and melt the polar stratospheric clouds, releasing considerable chlorine-based compounds, which drives ozone damage.

Ozone can be destroyed by a number of free radical catalysts, the most important of which are the hydroxyl radical (OH), nitric oxide radical (NO), chlorine radical (Cl) and bromine radical (Br) - all of these forms have an unpaired electron and are thus extremely reactive.

Once in the stratosphere, ultraviolet light acts to liberate these free radical catalysts from parent compounds. Chlorine for example acts to remove an oxygen atom from ozone creating 'O' and 'O2' - the 'O' then combines with chlorine to produce chlorine monoxide (ClO) and ClO then acts to convert to Cl and 2 sets of O2. Cl is then free to repeat the cycle.

It is calculated that a CFC molecule takes an average of about five to seven years to go from the ground level up to the upper atmosphere, and it can stay there for between 20 -100 years, destroying up to one hundred thousand ozone molecules during that time.

Ozone layer depletion: a happy ending to this story?

The ozone story offers hope for mankind in showing that concerted unilateral action can make a difference.

A gradual trend toward ozone layer

"healing" was widely reported in 2016 based on research by UK and US scientists.

The ozone layer is expected to begin to recover in coming decades due to declining ozone-depleting substance concentrations.

The Antarctic ozone hole is expected to continue for decades but ozone concentrations in the lower stratosphere over Antarctica are expected to increase by 5–10 percent by 2020 and to eventually return to pre-1980 levels by about 2060–2075.

The adoption and strengthening of the Montreal Protocol (which was drawn up 1987 but came into effect in 1989) has to take major credit for this reversal of fortunes.

As a result of the protocol harmful substances are being gradually removed from the atmosphere; since peaking in 1994, the Effective Equivalent Chlorine (EECl) level in the atmosphere had dropped by about 10 percent by 2008.

The phase-out of CFCs means that nitrous oxide (N2O), which is not covered by the Montreal Protocol, has become the most highly emitted ozone-depleting substance and is expected to remain so throughout the 21st century.

A 2005 IPCC review of ozone observations and model calculations concluded that the global amount of ozone has now approximately stabilised.

The discovery of the Antarctic ozone hole; Jonathan Shanklin, Meteorologist at the British Antarctic Survey, was one of the team that discovered the ozone hole in 1985. In this video, Jonathan reveals how this significant discovery was made and talks about the effectiveness of an international treaty, the Montreal Protocol, which places strict controls on ozone-destroying substances.

Credit: British Antarctic Survey.

Effects of ozone layer depletion

Ozone layer depletion effects on human health

Basal and squamous cell carcinomas

The most common forms of skin cancer in humans, basal and squamous cell carcinomas, have been strongly linked to UVB exposure. The mechanism by which UVB induces these cancers is well understood—absorption of UVB radiation causes replication problems in DNA molecules.

These cancers are relatively mild and rarely fatal, although the treatment of squamous cell carcinoma sometimes requires extensive reconstructive surgery. By combining epidemiological data with results of animal studies, scientists have estimated that every one percent decrease in long-term stratospheric ozone would increase the incidence of these cancers by two percent.

Malignant melanoma

Another form of skin cancer, malignant melanoma, is much less common but far more dangerous, being lethal in about 15–20 percent of the cases diagnosed. The relationship between malignant melanoma and ultraviolet exposure is not yet fully understood, but it appears that both UVB and UVA are involved.

Because of this uncertainty, it is difficult to estimate the effect of ozone depletion on melanoma incidence. One study showed that a 10 percent increase in UVB radiation was associated with a 19 percent increase in melanomas for men and 16 percent for women.

A study of people in Punta Arenas, at the southern tip of Chile, showed a 56 percent increase in melanoma and a 46 percent increase in nonmelanoma skin cancer over a period of seven years, along with decreased ozone and increased UVB levels.

Cortical cataracts

Epidemiological studies suggest an association between ocular cortical cataracts and UVB exposure, using crude approximations of exposure and various cataract assessment techniques.

A detailed assessment of ocular exposure to UVB was carried out in a study on Chesapeake Bay Watermen, where increases in average annual ocular exposure were associated with increasing risk of cortical opacity. In this highly exposed group of predominantly white males, the evidence linking cortical opacities to sunlight exposure was the strongest to date. Based on these results, ozone depletion is predicted to cause hundreds of thousands of additional cataracts by 2050.

Ozone layer depletion effects on the environment

Effects on non-human animals

A November 2010 report by scientists at the Institute of Zoology in London found that whales off the coast of California have shown a sharp rise in sun damage, and these scientists "fear that the thinning ozone layer is to blame".

The study photographed and took skin biopsies from over 150 whales in the Gulf of California and found "widespread evidence of epidermal damage commonly associated with acute and severe sunburn", having cells that form when the DNA is damaged by UV radiation.

The findings suggest "rising UV levels as a result of ozone depletion are to blame for the observed skin damage, in the same way that human skin cancer rates have been on the increase in recent decades."

Effects on crops

An increase of UV radiation would be expected to affect crops. A number of economically important species of plants, such as rice, depend on cyanobacteria residing on their roots for the retention of nitrogen.

Cyanobacteria are sensitive to UV radiation and would be affected by its increase."Despite mechanisms to reduce or repair the effects of increased ultraviolet radiation, plants have a limited ability to adapt to increased levels of UVB, therefore plant growth can be directly affected by UVB radiation."

Ozone depletion and ultraviolet light

Ozone, while a minority constituent in Earth's atmosphere, is responsible for most of the absorption of UVB radiation. When stratospheric ozone levels decrease, higher levels of UVB reach the Earth’s surface. UV-driven phenolic formation in tree rings has dated the start of ozone depletion in northern latitudes to the late 1700s.

In October 2008, the Ecuadorian Space Agency published a report called HIPERION, a study of the last 28 years data from 10 satellites and dozens of ground instruments around the world among them their own, and found that the UV radiation reaching equatorial latitudes was far greater than expected, with the UV Index climbing as high as 24 in some very populated cities; the World Health Organisation considers 11 as an extreme index and a great risk to health.

The report concluded that depleted ozone levels around the mid-latitudes of the planet are already endangering large populations in these areas.

Increased tropospheric ozone

Increased surface UV leads to increased tropospheric ozone. Ground-level ozone is generally recognized to be a health risk, as ozone is toxic due to its strong oxidant properties.

The risks are particularly high for young children, the elderly, and those with asthma or other respiratory difficulties. At this time, ozone at ground level is produced mainly by the action of UV radiation on combustion gases from vehicle exhausts.

Ozone depletion and global warming

The same carbon dioxide-driven processes that produce global warming is expected to cool the stratosphere. This cooling, in turn, is expected to produce a relative increase in ozone (O3) depletion in polar area and the frequency of ozone holes.

Conversely, ozone depletion impacts on the climate system. There are two opposing effects: reduced ozone causes the stratosphere to absorb less solar radiation, thus cooling the stratosphere while warming the troposphere; the resulting colder stratosphere emits less long-wave radiation downward, thus cooling the troposphere. Overall, the cooling dominates.

One of the strongest predictions of the greenhouse effect is that the stratosphere will cool.

Ozone layer depletion solutions

Government actions to reduce ozone layer depletion

After a 1976 report by the United States National Academy of Sciences concluded that credible scientific evidence supported the ozone depletion hypothesis a few countries, including the United States, Canada, Sweden, Denmark, and Norway, moved to eliminate the use of CFCs in aerosol spray cans.

In 1985 20 nations, including most of the major CFC producers, signed the Vienna Convention for the Protection of the Ozone Layer, which established a framework for negotiating international regulations on ozone-depleting substances.

That same year, the discovery of the Antarctic ozone hole was announced, causing a revival in public attention to the issue. In 1987, representatives from 43 nations signed the Montreal Protocol.

Meanwhile, the halocarbon industry shifted its position and started supporting a protocol to limit CFC production.

At Montreal, the participants agreed to freeze production of CFCs at 1986 levels and to reduce production by 50 percent by 1999.

After a series of scientific expeditions to the Antarctic produced convincing evidence that the ozone hole was indeed caused by chlorine and bromine from manmade organohalogens, the Montreal Protocol was strengthened at a 1990 meeting in London.

The participants agreed to phase out CFCs and halons entirely (aside from a very small amount marked for certain "essential" uses, such as asthma inhalers) by 2000 in non-Article 5 countries and by 2010 in Article 5 (less developed) signatories. At a 1992 meeting in Copenhagen, the phase-out date was moved up to 1996.

Personal actions to reduce ozone layer depletion

Pesticides may be an easy solution for getting rid of weed, but are harmful for the ozone layer. The best solution for this would be to try using natural remedies, rather than heading out for pesticides. You can perhaps try to weed manually or mow your garden consistently so as to avoid weed-growth.

Usage of eco-friendly and natural cleaning products for household chores is a great way to prevent ozone depletion. This is because many of these cleaning agents contain toxic chemicals that interfere with the ozone layer. A lot of supermarkets and health stores sell cleaning products that are toxic-free and made out of natural ingredients.

A very easy way to control ozone depletion would be to limit or reduce the amount of driving as vehicular emissions eventually result in smog which is a culprit in the deterioration of the ozone layer. Car pooling, taking public transport, walking, using a bicycle would limit the usage of individual transportation. It would be a great option to switch to cars/vehicles that have a hybrid or electric zero-emission engine.

Check your fire extinguishers to find active ingredients. If “halon” or “halogenated hydrocarbon” is the main ingredient, find a hazardous waste center at which to recycle it or call your local fire department for instructions on how to dispose of it. Replace it with a model without this harmful ozone-depleting chemical.

Don’t buy aerosol products with chlorofluorocarbons. Although CFCs have been banned or reduced in many applications, the only way to be sure is to check the label on all your hairsprays, deodorants and household chemicals. Opt for pump spray products over pressurized cans, to further reduce your chance of buying CFCs.

Dispose of pre-1995 refrigerators, freezers, and air conditioning units properly. These devices use chlorofluorocarbons to function, so leaks release the chemical into the atmosphere.

Ozone layer depletion news

For the latest ozone depletion news stories and other environmental news, check out our news page.

Ozone depletion news from ScienceDaily.com.

Ozone layer depletion facts

Ozone depletion is caused through 2 distinct types of actions

The first action is a general decline in stratospheric ozone levels, the second is a markedly larger depletion event which happens in spring of each year around the poles. These springtime events are capable of creating ozone 'holes'.

3 forms (or allotropes) of oxygen are involved in the ozone-oxygen cycle

Atomic oxygen (O), oxygen gas (O2) and ozone (O3) - also known as triatomic oxygen.

A single chlorine atom can destroy over 100,000 atoms of ozone

Chlorine in radical form (with an unpaired electron) is extremely reactive. Once in the stratosphere, ultraviolet light acts to liberate chlorine (Cl) from parent compounds. The chlorine atom acts to remove an oxygen atom from ozone creating 'O' and 'O2' - the 'O' then combines with chlorine to produce chlorine monoxide (ClO) and ClO then acts to convert to Cl and 2 sets of O2. Cl is then free to repeat the cycle.

Antarctic ozone can reduce by as much as 65% in springtime, arctic ozone has fallen by as much as 50% but is typically around the 30% mark

The ozone depletion impact at the antarctic pole is greater due to the role played by polar stratospheric clouds - the surface of these clouds aid chemical reactions which accelerate the ozone destruction.

Ozone Holes News -- ScienceDaily

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